1. Field of the Invention
This invention relates to a process for the liquid phase separation and recovery of arabinose from mixtures containing same. More particularly and in a preferred embodiment, this invention relates to such a separation by selective adsorption onto certain types of zeolitic molecular sieves from sugar mixtures containing arabinose.
2. Description of the Prior Art
The carbohydrate chemistry of the human body centers around sugars with `D` configurations. No human enzyme can synthesize or digest sugars of `L` configurations. On the other hand, the non-enzymatic chemistry and general properties of L- sugars should be essentially identical to their D- counterparts. It is this combination which is expected to make L- counterparts of such common sugars as L-fructose, L-glucose and L-sucrose ideal diet (i.e., non-nutritive) sweeteners, because they should taste like D- sugars and should be safe, yet cannot be metabolized by human enzymes.
L-fructose, L-glucose and L-sucrose do not occur naturally, but naturally-occuring L-arabinose can be used to make L-glucose which, in turn, can be isomerized to L-fructose which, in turn, can react with L-glucose to make L-sucrose (see, e.g., CHEMTECH, August, 1979, pp. 501 and 511).
L-arabinose is a five-carbon sugar, which can react with cyanide or nitromethane to extend the carbon chain length to six and, in further reactions, remove nitrogen to produce a mixture of L-glucose and L-mannose. Both glucose and mannose are not good sweeteners; L-fructose is a good sweetener. The mixture of sugars has to be separated and further transformed into sweeter sugars. L-mannose can be isomerized to L-glucose and L-glucose can be isomerized to L-fructose.
In nature, L-arabinose often exists as the hemicelluloses L-araban and L-araban-D-galactan, which are found in mesquite gum, cherry gum, peach gum, rye and wheat bran, beet pulp and in the wood of coniferous trees. In some of these sources, the content of these hemicelluloses is substantial. For example, 20-30% of the pectic substance in sugar beet is araban. The wood of genus Larix may contain 25% L-araban-D-galactan. Araban-galactans are water-soluble. They can be isolated in good yield by extraction from wood with water before delignification.
L-arabinose can be obtained by hydrolysis of beet pulp, which gives a mixture of L-arabinose, D-galactose, and sucrose. If stronger hydrolysis conditions are used, the product mixture will also contain glucose and fructose. If wood is used as a raw material, the product mixture will contain mannose and xylose. In order to realize the potential of L-sugars as diet sweeteners, the separation problem must be solved. First, the L-arabinose has to be separated from the other sugars in the hydrolyzate. Second, L-glucose has to be separated from L-mannose. Commonly-assigned, copending U.S. patent application Ser. No. 454,646, filed on even date herewith describes an efficient method of separating mannose from glucose and other sugars by adsorption.
The traditional method of L-arabinose purification consists of several steps: first, other sugars are removed by fermentation with yeast; then, some of the fermentaton products are removed by anion exchange and L-arabinose is recovered by crystallization (See, e.g., V. Tibensky, Czech. Pat. No. 153,378, (1974); C. A., (1975), Vol. 82, 17065r; and R. L. Whistler and M. L. Wolfrom, Ed., Method of Carbohydrate Chem., pp. 71-77, Academic Press, 1962). It is the purpose of this invention to provide an efficient method of recovering arabinose from a mixture of sugars.